However, the game displayed a message on the screen telling her she had also won a bonus of $41,797,550.16 - a message the casino claimed was the machine malfunctioning.

Ms McKee took the casino to court when they refused to pay out on the basis that on-screen rules stated that "malfunction voids all pays and plays".

Meanwhile, the Iowa Racing and Gaming Commission (IRGC) sent the machine's software and hardware to an independent laboratory for testing.

The lab determined that the software programme was designed to award bonus payments of up to $10,000. It could not establish how the machine had issued a multi-million pound bonus message but determined that the bonus display was "not valid".

Aristocrat Technologies, the manufacturer of the machine, said it had alerted casinos to the glitch and recommended that they disable the bonus feature as a precautionary measure. It appeared that the casino Ms McKee visited did not do this.

Ms McKee sued the casino in 2012 for breach of contract and consumer fraud, but her suit was finally rejected on 24 April 2015.

"I had my doubts from the start, because that's a lot of money for a penny machine," she told the Chicago Tribune after the ruling.

"I was hoping to help my children out financially, but it wasn't meant to be."